tidied up objects and wrote docs for object creation

docs/Objects.md

src/tg/detail/functions/aabb.hh

src/tg/detail/functions/area.hh

src/tg/detail/functions/centroid.hh

src/tg/detail/functions/closest_points.hh

src/tg/detail/functions/contains.hh

src/tg/detail/functions/coordinates.hh

src/tg/detail/functions/distance.hh

src/tg/detail/functions/length.hh

src/tg/detail/functions/normal.hh

src/tg/detail/functions/project.hh

src/tg/detail/functions/rasterize.hh

src/tg/detail/functions/uniform.hh

src/tg/detail/functions/volume.hh

src/tg/detail/operators/ops_triangle.hh

src/tg/types/objects/box.hh

src/tg/types/objects/cylinder.hh

src/tg/types/objects/frustum.hh

src/tg/types/objects/halfspace.hh

src/tg/types/objects/hyperplane.hh